Saturday, 19 February 2011

Norman Robert Pogson - Astronomer & The Great Son of Madras

Greatest Anglo - Indian Astronomer. Son of Madras. Former head of Madras Observatory, Nungambakkam Village, Madras.

Dr. Norman Robert Pogson PhD CIE (March 23, 1829 in Nottingham – June 23, 1891 in Madras) is an Indian English astronomer. His tomb is in St. George's Cathedral, Madras
(I also have a doubt it may be located in graveyard for English Elites in Bodyguard Lines Road near Stanley Viaduct). Recently after reading book Madras Discovered by Sri. S. Muthiah, I decided to write an article on this great Astronomer of Madras. I searched a lot on this gentleman and was only able to collect a few points which I posted in Wikipedia and reproduce the same here for view of the world. The Wikipedia article was later seems amended by some family member of the astronomer and can be read here.

By the time he was 18 years old, he had computed the orbits of two comets. He became an assistant at Radcliffe Observatory in Oxford, England in 1851. In 1860 he travelled to Madras, India, becoming the Government Astronomer. At the Madras Observatory he produced the Madras Catalogue of 11,015 stars. He also discovered five asteroids and six variable stars.

His most notable contribution was to note that in the stellar magnitude system introduced by the Greek astronomer Hipparchus, stars of the first magnitude were a hundred times as bright as stars of the sixth magnitude. Pogson's suggestion in 1856 was to make this a standard; thus, a first magnitude star is 1001/5 or about 2.512 times as bright as a second magnitude star. This fifth root of 100 is known as Pogson's Ratio.

The magnitude relation is given as follows:

m1 - m2 = -2.5 log10 (L1 / L2)

where m is the stellar magnitude and L is the luminosity, for stars 1 and 2.

In 1868 and 1871, Pogson joined the Indian solar eclipse expeditions. In 1872, he observed an object (recorded as X/1872 X1) which he believed to be a return of Biela's Comet.

During his career he discovered a total of eight asteroids and 21 variable stars. He headed the Madras Observatory for 30 years until his death.


The following celestial features are named after him:

* Asteroid 1830 Pogson.
* The crater Pogson on the Moon.


* Magnitudes of Thirty-six of the Minor Planets for the first day of each month of the year 1857, N. Pogson, MNRAS 17 pp 12 1856 in which Pogson first introduced his magnitude system

Norman Robert Pogson (1829-1891) formalized Hipparchus' magnitude system in 1856 by stating that a difference of 5 magnitudes (1st to 6th, for example) is equal to brightness ratio of 100. In other words, a 1st-magnitude star is in actuality 100 times brighter than a 6th-magnitude star. Pogson didn't just come up with this scheme out of the blue: he made careful measurements using "the method of reduced apertures" to determine at what aperture stars of a given magnitude first became invisible to the eye looking through the telescope.

The magnitude scale is logarithmic. What this means is that a series of numbers that are multiples of a given number can be represented by a linear progression of exponents. The advantage of such a system is that a large range of numbers can be represented by using a small range of numbers, as shown in the following two examples.

If a difference of 5 magnitudes equals a factor of 100 in brightness, then a difference in one magnitude equals a factor of approximately 2.512 (exactly 1001/5 = the fifth root of 100) in brightness. So, a 1.0-magnitude star is 2.512 times as bright as a 2.0-magnitude star, and a 1.0 magnitude star is 100 times as bright as a 6.0-magnitude star (2.512 * 2.512 * 2.512 * 2.512 * 2.512 = 100).

The Hipparchus/Pogson magnitude system reflects the approximately logarithmic nature of human vision. Though a 1.0-magnitude star appears to us to be about twice as bright as a 2.0-magnitude star, if we were to actually measure the amount of energy coming from the two stars we would find that we receive 2.512 times as much energy from the 1.0-magnitude star as we do from the 2.0-magnitude star.

Asteroids discovered: 8
42 Isis May 23, 1856
43 Ariadne April 15, 1857
46 Hestia August 16, 1857
67 Asia April 17, 1861
80 Sappho May 2, 1864
87 Sylvia May 16, 1866
107 Camilla November 17, 1868
245 Vera February 6, 1885

All these were identified from Madras
* Magnitudes of Thirty-six of the Minor Planets for the first day of each month of the year 1857

A link on his works:

My article on Sir Pogson in Practical Astronomy Magazine July 2011 issue

His other photos:


Michael said...

Thanks for this excellent piece and for your wikipedia page. Really interesting. I am currently writing a book for Springer, and this has given me exactly the information I needed


Shyamal L. said...

Was he related to W. N. Pogson who was an architect in the Madras Presidency?

Dhinakar said...

Shyamal L: You may get the details from the book in this link :

R Gopu said...

Very nice essay, good to know that Pogson got the magnitude system universalised. Is there any such information about J Goldingham, who worked in that period?